For cleaning the teeth, in order to loosen dental film or plaque on the tooth surfaces, numerous electrically driven toothbrushes are available, performing different brushing movements. These vary from a planar elliptical movement of the bristle ends with a major axis of approximately 2 mm and a minor axis of approximately 10 mm, via an oscillatory movement of the brush surface about the longitudinal axis of the handle, and a combination of an oscillatory movement and a short axial movement of 1-2 mm, to a rotation of cylindrical tufts of bristles about their longitudinal axes. A further group of electrically driven mechanical tooth-cleaning appliances effects cleaning by a rotation of the individual tufts of bristles and/or a combination of this movement with a pivotal movement of the entire brush. The movement frequency is generally between 20 and 50 Hz.
As a result of the rapid reciprocatory movement of the brush the cleaning action is effective only at those spots which as a rule are readily accessible at any rate, i.e. the surfaces of the teeth.
The combination of large amplitudes with brush movement frequencies of between 20 and 50 Hz leads to the following symptoms or drawbacks:
At step-like surface structures, for example at the transition between the gingival border and the tooth, blind comers are formed where the bristle ends do not reach the surface to be cleaned. As a result, these areas are not cleaned or not cleaned properly. PA1 Owing to the large amplitude associated with the high frequency the brush behaves as a brush whose individual filaments are less flexible and dynamically stiffer. The maximum force exerted on, for example, the gums then exceeds the now generally accepted permissible value of approximately 2 N and leads to gum injury. PA1 Some of the bristles get caught and are almost immobilized, exerting an impermissible pressure on the gums when the brush passes through the center position. PA1 The interdental spaces are not cleaned satisfactorily because the bristles do not reach into the interdental spaces as a result of their dynamic stiffening. The bristles remain on the prominent tooth surfaces so that the deeper situated interdental spaces and the approximal surfaces are skipped. Neither do they reach into the gingival sulcus.
The cleaning action of the tooth-brush decreases distinctly at lower frequencies. Moreover, as the frequency decreases the feel of the tooth-brush diminishes, which also leads to poor cleaning results.
With tooth-brushes of the above-mentioned type having separately rotating tufts the interdental spaces are cleaned but an undesired side-effect of these brushes is that they cause a substantial attrition of the dentine at the tooth necks.